Wind energy systems, which are now being used increasingly as alternative energy sources as energy resources disappear, are normally set up on land or at sea, close to the coast. One such wind energy system is disclosed in WO 00/74198 A1. The wind energy system has at least two wind rotors, with each rotor being mechanically connected to a generator, which it drives. Each of the generators is connected to an associated passive rectifier unit. All the rectifier units also have an energy storage circuit on their DC voltage sides, with each energy storage circuit being formed by appropriate inductances. However, due to their large and complex structure, these inductances result in additional material costs and require a correspondingly large amount of space. Each energy storage circuit is followed by a step-up controller for matching the direct current to the corresponding rectifier unit. The energy storage circuits in WO 00/74198 A1, together with the downstream step-up controllers, are connected in parallel to a busbar system and feed electrical energy into a transmission system, with the transmission system normally being in the form of a two-phase busbar. For a long transmission system, a DC/DC controller is provided on the input side for matching to the high DC voltage which is required for low-loss power transmission. The transmission system is connected to a network coupling device, which has an input circuit formed by a DC voltage capacitance. Furthermore, the DC voltage side of an inverter for the network coupling device is connected to the input circuit, with the AC voltage side of the inverter being coupled via a network transformer to a conventional electrical supply network.
Problems occur with a wind energy system such as this when one or more rectifier units and/or the inverter for the network coupling device fail, and the transmission system and hence all the energy storage circuits which are connected to it and the input circuit of the network coupling device are short-circuited. One known solution is for all of the energy storage circuits to be actively short-circuited by means of their step-up controllers, in particular by means of a thyristor in the appropriate step-up controller, and for the input circuit to be short-circuited by means of the inverter. Simultaneous short-circuiting results in the short-circuit currents being distributed uniformly between all the rectifier units and the inverter. The electrical AC voltage supply network is then disconnected in order to interrupt the short-circuit currents, by means of a conventional network circuit breaker. If one rectifier unit is defective, this must then be disconnected in order to allow operation of the wind energy system to be resumed. However, with disconnection such as this, in particular of the appropriate energy storage circuit, it must be possible to cope with the short-circuit current which flowed prior to this until the associated generator has been braked to rest. In the wind energy system as claimed in WO 00/74198 A1, no provision is made for any capability for such disconnection from the energy storage circuit, which is accordingly not possible. Furthermore, signals must be transmitted quickly to the step-up controllers and to the inverter in order to make it possible to initiate the simultaneous active short circuit, as mentioned above, in the event of a defect in one or more rectifier units and/or in the inverter. However, signal transmission such as this is associated with a high level of complexity in terms of additional components and material, particularly if such signals are intended to be transmitted over a long distance. Overall, in a wind energy system as claimed in WO 00/74198 A1, further operation of the components which are not defective or have not failed without any interruption is impossible in the event of a failure or a defect in one or more of the rectifier units and/or in the inverter for the network coupling device.